Latest research in football - week 17 - 2017

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Talent identification and recruitment in youth soccer: Recruiter's perceptions of the key attributes for player
recruitmentReference: PLoS One. 2017 Apr 18;12(4):e0175716. doi: 10.1371/journal.pone.0175716. eCollection 2017.Authors: Larkin P, O'Connor DDownload link:http://journals.plos.org/plosone/article/file?id=10.1371/journal.pone.0175716&type=printableSummary: Using the modified Delphi method, we aimed to understand the attributes youth coaches and recruiters perceive as important when identifying skilled youth performance at
the entry level of representative soccer in Australia (i.e., Under 13 years). Furthermore, we also aimed to describe the current methods youth coaches and recruiters use to assess and identify
these attributes in youth players. Australian regional youth technical directors and coaches (n = 20) completed a three stage process, including an initial interview and two subsequent
questionnaires, whereby attributes and qualities associated with talent identification were rated and justified according to the importance for youth player performance and talent identification.
Results indicate a hierarchy of attributes recruiters perceive as important for Under 13 soccer performance, including technical (i.e., first touch, striking the ball, one-versus-one ability, and
technical ability under pressure), tactical (i.e., decision-making ability) and psychological attributes (i.e., coachability and positive attitude). In addition, the findings indicated attributes
and qualities not emphasised within the talent identification process including, physiological, anthropometrical, sociological and several psychological attributes. It is suggested talent
recruiters apply a holistic multidisciplinary approach to talent identification, with the current findings potentially providing initial evidence to suggest recruiters do consider numerous
attributes when selecting and identifying youth players.

#2 Unilateral jumps in different directions: a novel assessment of soccer-associated power?Reference: J Sci Med Sport. 2017 Mar 29. pii: S1440-2440(17)30348-1. doi: 10.1016/j.jsams.2017.03.016. [Epub ahead of print]Authors: Murtagh CF, Vanrenterghem J, O'Boyle A, Morgans R, Drust B, Erskine RMSummary: We aimed to determine whether countermovement jumps (CMJs; unilateral and bilateral) performed in different directions assessed independent lower-limb power qualities,
and if unilateral CMJs would better differentiate between elite and non-elite soccer players than the bilateral vertical (BV) CMJ. Elite (n=23; age, 18.1±1.0years) and non-elite (n=20; age,
22.3±2.7years) soccer players performed three BV, unilateral vertical (UV), unilateral horizontal-forward (UH) and unilateral medial (UM) CMJs. Jump performance (height and projectile range),
kinetic and kinematic variables from ground reaction forces, and peak activation levels of the vastus lateralis and biceps femoris (BF) muscles from surface electromyography, were compared
between jumps and groups of players. Peak vertical power (V-power) was greater in BV (220.2±30.1W/kg) compared to UV (144.1±16.2W/kg), which was greater than UH (86.7±18.3W/kg) and UM
(85.5±13.5W/kg) (all, p<0.05) but there was no difference between UH and UM (p=1.000). Peak BF EMG was greater in UH compared to all other CMJs (p≤0.001). V-power was greater in elite than
non-elite for all CMJs (p≤0.032) except for BV (p=0.197). Elite achieved greater UH projectile range than non-elite (51.6±15.4 vs. 40.4±10.4cm, p=0.009). We have shown that UH, UV and UM CMJs
assess distinct lower-limb muscular power capabilities in soccer players. Furthermore, as elite players outperformed non-elite players during unilateral but not BV CMJs, unilateral CMJs in
different directions should be included in soccer-specific muscular power assessment and talent identification protocols, rather than the BV CMJ.

#3 Range limitation in hip internal rotation and fifth metatarsal stress fractures (Jones fracture) in professional football
playersReference: Knee Surg Sports Traumatol Arthrosc. 2017 Apr 25. doi: 10.1007/s00167-017-4552-4. [Epub ahead of print]Authors: Saita Y, Nagao M, Kawasaki T, Kobayashi Y, Kobayashi K, Nakajima H, Takazawa Y, Kaneko K, Ikeda HSummary: The purpose of the study was to identify unknown risk factors associated with fifth metatarsal stress fracture (Jones fracture). A case-controlled study was conducted
among male Japanese professional football (soccer) players with (N = 20) and without (N = 40) a history of Jones fracture. Injury history and physical examination data were
reviewed, and the two groups were compared. Univariate and multivariate logistic regression controlling for age, leg dominance and body mass index were used to obtain odds ratios (ORs) and 95%
confidence intervals (CIs) to describe the association between physical examination data and the presence or absence of Jones fractures. From 2000 to 2014, among 162 professional football club
players, 22 (13.6%; 21 Asians and one Caucasian) had a history of Jones fracture. Thirteen out of 22 (60%) had a Jones fracture in their non-dominant leg. The mean range of hip internal rotation
(HIR) was restricted in players with a history of Jones fracture [25.9° ± 7.5°, mean ± standard deviation (SD)] compared to those without (40.4° ± 11.1°,
P < 0.0001). Logistic regression analyses demonstrated that HIR limitation increased the risk of a Jones fracture (OR = 3.03, 95% CI 1.45-6.33, P = 0.003).
Subgroup analysis using data prior to Jones fracture revealed a causal relationship, such that players with a restriction of HIR were at high risk of developing a Jones fracture [Crude OR (95%
CI) = 6.66 (1.90-23.29), P = 0.003, Adjusted OR = 9.91 (2.28-43.10), P = 0.002]. In addition, right HIR range limitation increased the risks of developing
a Jones fracture in the ipsilateral and the contralateral feet [OR = 3.11 (1.35-7.16) and 2.24 (1.22-4.12), respectively]. Similarly, left HIR range limitation increased the risks in
the ipsilateral or the contralateral feet [OR (95% CI) = 4.88 (1.56-15.28) and 2.77 (1.08-7.08), respectively]. The restriction of HIR was associated with an increased risk of
developing a Jones fracture. Since the HIR range is a modifiable factor, monitoring and improving the HIR range can lead to prevent reducing the occurrence of this fracture.

#4 Testosterone and cortisol responses in male soccer players: The effect of home and away venuesReference: Physiol Behav. 2017 Apr 21. pii: S0031-9384(16)30994-5. doi: 10.1016/j.physbeh.2017.04.021. [Epub ahead of print]Authors: Fothergill M, Wolfson S, Neave NSummary: The present studies examined the influence of playing venue on psychobiological responses in male soccer players. Many studies have demonstrated the existence of a home
advantage, wherein teams perform better at home than away. A recent focus has attempted to explain this advantage from a psychobiological perspective, with studies showing hormonal differences
with regard to venue, game outcome, dominance and perceived stress. Two studies investigated testosterone and cortisol responses in relation to home and away venues. In an initial study of 18
male elite Premier League academy soccer players (age, 17.47, SD, 64), salivary cortisol levels were monitored in two competitive matches, both at home and away. Higher post-game cortisol levels
were observed at home (p=0.002), with the team winning all its games. In a second study involving a 12 semi-professional group of players (age, 23.17, SD, 3.8), the same post-game cortisol
findings at home were replicated (p=0.001), with this team losing all its games. No effects were observed for testosterone in either study. The results extend earlier research findings on the
complex relationship which surrounds the psychobiological impact on the home advantage. The findings suggest that higher levels of stress are experienced by home players in their home
matches.

#5 Wellbeing perception and the impact on external training output among elite soccer playersReference: J Sci Med Sport. 2017 Apr 13. pii: S1440-2440(17)30360-2. doi: 10.1016/j.jsams.2017.03.019. [Epub ahead of print]Authors: Malone S, Owen A, Newton M, Mendes B, Tiernan L, Hughes B, Collins KSummary: The objective of the investigation was to observe the impact of player wellbeing on the training output of elite soccer players. Forty-eight soccer players (age:
25.3±3.1years; height: 183±7cm; mass: 72±7kg) were involved in this single season observational study across two teams. Each morning, pre-training, players completed customised perceived
wellbeing questionnaires. Global positioning technology devices were used to measure external load (total distance, total high-speed running distance, high speed running, player load, player load
slow, maximal velocity, maximal velocity exposures). Players reported ratings of perceived exertion using the modified Borg CR-10 scale. Integrated training load ratios were also analysed for
total distance:RPE, total high speed distance:RPE player load:RPE and player load slow:RPE respectively. Mixed-effect linear models revealed significant effects of wellbeing Z-score on external
and integrated training load measures. A wellbeing Z-score of -1 corresponded to a -18±2m (-3.5±1.1%), 4±1m (-4.9±2.1%,) 0.9±0.1kmh-1 (-3.1±2.1%), 1±1 (-4.6±2.9%), 25±3AU (-4.9±3.1%) and 11±0.5AU
(-8.9±2.9%) reduction in total high speed distance, high speed distance, maximal velocity, maximal velocity exposures, player load and player load slow respectively. A reduction in wellbeing
impacted external:internal training load ratios and resulted in -0.49±0.12mmin-1, -1.20±0.08mmin-1,-0.02±0.01AUmin-1 in total distance:RPE, total high speed distance:RPE and player load slow:RPE
respectively. The results suggest that systematic monitoring of player wellbeing within soccer cohorts can provide coaches with information about the training output that can be expected from
individual players during a training session.

#6 Reliability and Validity of a New Test of Agility and Skill for Female Amateur Soccer PlayersReference: J Hum Kinet. 2017 Mar 12;56:219-227. doi: 10.1515/hukin-2017-0039. eCollection 2017.Authors: Kutlu M, Yapici H, Yilmaz ASummary: The aim of this study was to evaluate the Agility and Skill Test, which had been recently developed to assess agility and skill in female athletes. Following a 10 min
warm-up, two trials to test the reliability and validity of the test were conducted one week apart. Measurements were collected to compare soccer players' physical performance in a 20 m sprint, a
T-Drill test, the Illinois Agility Run Test, change-of-direction and acceleration, as well as agility and skill. All tests were completed following the same order. Thirty-four amateur female
soccer players were recruited (age = 20.8 ± 1.9 years; body height = 166 ± 6.9 cm; body mass = 55.5 ± 5.8 kg). To determine the reliability and usefulness of these tests, paired sample t-tests,
intra-class correlation coefficients, typical error, coefficient of variation, and differences between the typical error and smallest worthwhile change statistics were computed. Test results
showed no significant differences between the two sessions (p > 0.01). There were higher intra-class correlations between the test and retest values (r = 0.94-0.99) for all tests. Typical
error values were below the smallest worthwhile change, indicating 'good' usefulness for these tests. A near perfect Pearson correlation between the Agility and Skill Test (r = 0.98) was found,
and there were moderate-to-large levels of correlation between the Agility and Skill Test and other measures (r = 0.37 to r = 0.56). The results of this study suggest that the Agility and Skill
Test is a reliable and valid test for female soccer players and has significant value for assessing the integrative agility and skill capability of soccer players.

#7 Analysis of Motor Activities of Professional Soccer Players during the 2014 World Cup in BrazilReference: J Hum Kinet. 2017 Mar 12;56:187-195. doi: 10.1515/hukin-2017-0036. eCollection 2017.Authors: Chmura P, Andrzejewski M, Konefał M, Mroczek D, Rokita A, Chmura JSummary: The aim of the present study was to analyze motor activities of soccer players in seven consecutive rounds of matches of the 2014 World Cup in Brazil and to compare the
performance of the world champions, the German national team with other participating teams. The study sample comprised 905 observations of 340 soccer players, who played full-time matches in all
seven rounds of the tournament. The study was conducted using data collected from the Castrol Performance Index, a kinematic game analysis system that records movements of players with
semi-automatic cameras. The following variables were analyzed: total distance covered, the percentage of total distance covered at high intensity, the number of sprints, frequency of sprints and
peak running speed. A statistically significant increase (p ≤ 0.01) was noted in total distance covered, the percentage of distance covered at high intensity and total number of sprints, between
the quarter-finals and semi-finals of the World Cup tournament in Brazil. The German national team covered a significantly longer total distance (p ≤ 0.05) and had a greater percentage of
distance covered at high intensity (p ≤ 0.001) than players from other teams. The obtained results point to the necessity of development of players' aerobic endurance and speed-endurance
abilities while preparing for top-level soccer tournaments. Winning a soccer championship requires players to run longer mean total distances and longer distances at high intensity during a
single match.

#8 Effects of the off-Season Period on Field and Assistant Soccer Referees `Physical PerformanceReference: J Hum Kinet. 2017 Mar 12;56:159-166. doi: 10.1515/hukin-2017-0033. eCollection 2017.Authors: Castillo D, Cámara J, Castagna C, Yanci JSummary: The evolution of referees' physical fitness has been studied over one or several seasons, however, the variation of the physical performance between the end of the
competitive season (T1) and the start of the following pre-season (T2) has not been ascertained. Therefore, the aim of this study was to analyze the effects of the transition period on physical
performance variables (i.e. linear straight sprint, change of direction ability and endurance) in National Soccer Division referees. Forty-five Spanish referees volunteered to participate in this
study. Participants were classified according to competitive status, field referees (FR, n = 23) and assistant referees (AR, n = 22). A loss of performance (p < 0.05) was observed in the 20
and 30 m linear straight sprint between T1 and T2 in both FR (1.64-1.56%, d = 0.29 to 0.32) and AR (2.01-3.41%, d = 0.33 to 0.60). In T2 the FR significantly improved the distance covered (p <
0.05, 13.11%, d = 0.39) in the Yo-Yo Intermittent Recovery test (YYIR1). Besides, significant differences were observed between FR and AR in the distance covered (p < 0.05, -23.55%, d = -0.97)
in the YYIR1 test in T2. More research may be necessary to focus on the off-season period in order to implement specific training programs and consequently reduce the loss of sprint ability in
field and assistant referees and the decrease in cardiovascular fitness in assistant referees.

#9 Determination of Aerobic Performance in Youth Soccer Players: Effect of Direct And Indirect MethodsReference: J Hum Kinet. 2017 Mar 11;56:109-118. doi: 10.1515/hukin-2017-0028. eCollection 2017.Authors: Higino WP, Sorroche AS, de Mattos Falqueiro PG, Suzuki Lima YC, Higa CLSummary: This study was conducted to correlate and compare values for variables determined in indirect tests with the values determined directly in youth soccer players. The
study subjects were 27 youth soccer players (age 16.77 ± 0.75 years; body mass 63.29 ± 7.37 kg; body height 174.14 ± 8.46 cm) playing in the basic categories of a first division team at the
regional level of Brazilian soccer. Each subject was evaluated with the following tests: a) a treadmill test to directly determine values of VO2max and Vamax (Treadmill); b) an indirect Shuttle
Run Test (SRT); c) an indirect Carminatti's test (TCar). VO2max showed significantly different values in the Treadmill and the SRT (59.21 ± 5.88 and 50.67 ± 3.58 ml⋅kg-1⋅min-1, respectively).
Similarly, values obtained for VPeak in the treadmill test and for Vamax in TCar were different from values for SRT VPeak (15.01 ± 1.10, 14.92 ± 0.87 and 12.64 ± 0.62 km⋅h-1, respectively). A
correlation analysis showed a moderate relationship between values for VPeak TCar and VO2max determined on a treadmill (r = 0.46) and Vamax determined on a treadmill (r = 0.54). The analysis also
showed a high correlation between values of VO2max determined on the treadmill and VO2max evaluated in the SRT (r = 0.69), as well as VPeak determined in the SRT and VO2max tested on the
treadmill (r = 0.71), as well as between VPeak determined in the SRT and VO2max evaluated on the treadmill (r = 0.77). We concluded that the SRT underestimated values of VO2max and Vamax.
Additionally, VPeak TCar showed no difference compared to Vamax, although it did show a low correlation with it. In addition the SRT, even with high correlations, did not seem to be a great
predictor of aerobic fitness in youth soccer players.

#10 Effects of environmental temperature on physiological responses during submaximal and maximal exercises in soccer
playersReference: Integr Med Res. 2016 Sep;5(3):216-222. doi: 10.1016/j.imr.2016.06.002. Epub 2016 Jun 16.Authors: No M, Kwak HBDownload link:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5390419/pdf/main.pdfSummary: Although thermoregulation is effective in regulating body temperature under normal conditions, exercise or physical activity in extreme cold or heat exerts heavy stress
on the mechanisms that regulate body temperature. The purpose of this study was to investigate the effects of environmental temperature on physiological responses and endurance exercise capacity
during submaximal and maximal exercises in healthy adults. Nine male soccer players participated in this study. In this study, three environmental temperatures were set at 10 ± 1°C,
22 ± 1°C, and 35 ± 1°C with the same humidity (60 ± 10%). The participants cycled for 20 minutes at 60% maximum oxygen uptake (60% VO2max), and then exercise
intensity was increased at a rate of 0.5 kp/2 min until exhaustion at three different environmental conditions. Oxygen uptake and heart rate were lower in a moderate environment
(22 ± 1°C) than in a cool (10 ± 1°C) or hot (35 ± 1°C) environment at rest and during submaximal exercise, and were higher during maximal exercise
(p < 0.05). Minute ventilation was lower at 22 ± 1°C than at 10 ± 1°C or 35 ± 1°C at rest and during submaximal exercise, and no significant differences
were observed in minute ventilation during maximal exercise (p < 0.05). Blood lactate concentrations were lower at 22 ± 1 °C than at 10 ± 1°C or
35 ± 1°C at rest and during submaximal exercise, and were higher during maximal exercise (p < 0.05). Time to exhaustion during exercise was longer at 22 ± 1°C
than at 10 ± 1°C or 35 ± 1°C (p < 0.05). It is concluded that physiological responses and endurance exercise capacity are impaired under cool or hot conditions
compared with moderate conditions, suggesting that environmental temperature conditions play an important role for exercise performance.

American Football#1 Game Times and Higher Winning Percentages of West Coast Teams of the National Football League Correspond With Reduced Prevalence of Regular
Season Injury: Erratum.Reference: J Strength Cond Res. 2017 May;31(5):e72. doi: 10.1519/JSC.0000000000001851.Authors: no authors listed

#2 Acute Effect of Biomechanical Muscle Stimulation on the Counter-Movement Vertical Jump Power and Velocity in Division I Football
PlayersReference: J Strength Cond Res. 2017 May;31(5):1259-1264. doi: 10.1519/JSC.0000000000001136.Authors: Jacobson BH, Monaghan TP, Sellers JH, Conchola EC, Pope ZK, Glass RGSummary: Research regarding whole body vibration (WBV) largely supports such training augmentation in attempts to increase muscle strength and power. However, localized
biomechanical vibration has not received the same attention. The purpose of this study was to assess peak and average power before and after acute vibration of selected lower-body sites in
division I athletes. Twenty-one subjects were randomly assigned to 1 of 2 conditions using a cross-over design. Pretest consisted of a counter-movement vertical jump (VJ) followed by either
localized vibration (30 Hz) to 4 selected lower-body areas or 4 minutes of moderately low-resistance stationary cycling (70 rpm). Vibration consisted of 1 minute bouts at each lower-leg site for
a total of 4 minutes followed by an immediate post-test VJ. Repeated measures analysis of variance yielded no significant differences (p > 0.05) in either peak power or peak velocity.
Similarly, no significant differences were found for average power and velocity between conditions. It should be noted that, while not significant, the vibration condition demonstrated an
increase in peak power and velocity while the bike condition registered slight decreases. Comparing each of the post-VJ repetitions (1, 2, and 3) the vibration condition experienced significantly
greater peak power and velocity from VJ 1 to VJ 3 compared with the bike condition which demonstrated no significant differences among the post-test VJs. These results yielded similar, although
not statistically significant outcomes to previous studies using WBV. However, the novelty of selected site biomechanical vibration merits further investigation with respect to frequency,
magnitude, and duration of vibration.